Pneumatic tube carrier systems are a well-known means for the automated transport of materials between, for example, an origination location and any one of a plurality of destination locations. A typical system includes a number of pneumatic tubes interconnected in a network to transport carriers between user stations. Various blowers and transfer units provide the force and path control means, respectively, for moving the carriers through and from tube-to-tube within the network. Generally, transfer units move or divert pneumatic carries from a first pneumatic tube to a second pneumatic tube in order to route the pneumatic carrier between locations, or stations, in the network.
The pneumatic tubes forming the network of a pneumatic tube system may be arranged in any manner that allows the carriers to be transferred between various stations. Generally, systems include a number of individual stations interconnected to the network by a single pneumatic tube. The single pneumatic tube transfers carriers to and from the station under pressure and vacuum. Other portions of the network and/or certain stations may utilize dedicated unidirectional pneumatic tubes. It will be appreciated that the number and distances between stations in the network may be quite large. For instance, many large facilities (e.g., hospitals) incorporate pneumatic tube systems having dozens of user stations where the distance between the most distally located pair of stations may exceed several hundred yards or even several miles.
Large pneumatic tube systems often require a complex network of interconnected tubes. Further, to provide functionality to separate portions of such large systems, most such systems are divided into multiple zones. Typically, each zone includes a set of stations that receive pneumatic pressure and/or vacuum from a common blower. For instance, a transfer unit that receives pressure and/or vacuum from the common blower may connect to each station of such a zone. This transfer unit permits carriers received from a tube connected to one of the stations to be transferred to a tube associated with another of the stations. However, effective use of the pneumatic tube system requires connecting the different zones to permit inter-zone traffic (i.e., transfers from zone to zone).
To provide inter-zone connections, zones commonly connect to a specialized zone transfer unit. Such zone transfer units have heretofore required connecting each serviced zone with a dedicated input and output tube and have limited the expansion of the pneumatic system to a number of zones corresponding to the number of sets of inlet and outlet tubes of the zone transfer unit. Such dedicated interconnection, while providing effective inter-zone transport, results in complex tubing arrangements and often requires that a blower of a zone sending a carrier to another zone stand-by to deliver the carrier until a downstream path becomes available. This, of course, prevents the blower from processing other transactions. Stated otherwise, current inter-zone transfer units can result in various system inefficiencies.